1. Technical Field
The present invention generally relates to optical diffraction elements, particularly, to a diffraction grating structure and a method for manufacturing the same.
2. Discussion of Related Art
Diffraction gratings are widely used in technology. In particular, the diffraction gratings serve as dispersive elements for spectrum analyzers and are also often used in laser devices serving to select, tune, and expand the light spectrums of the laser devices. In integrated optics and light communication, a diffraction grating is an advantageous optical-coupling element.
Currently, diffraction gratings are manufactured by one of two methods. The first method is using ruling engines. Diffraction gratings manufactured with a ruling engine are called mechanically ruled gratings. Grooves of the mechanical ruled grating have different characteristics because of ability of the ruling engines. Some various stray lines produced in a photographic side of the grating can effect application of the grating in high impact spectrometers. Using ruling to manufacture the ruled grating is costly, requiring a lot of time and strict control of the production environment, so that application of the mechanical ruled grating is limited.
The second method involves laser technology. Diffraction gratings made this way are called holographic gratings and have sinusoidal grooves. For holographic gratings, lasers are used on a substrate to etch film coated thereon, to form a regular pattern of grooves, and the grooves may then be bombarded with an ion beam to produce a blazed grating and to enhance grating diffraction efficiency.
The diffraction gratings manufactured by the above two methods are usually a single surface structure. Light beams passing through the gratings cannot be converted from a low spatial frequency to a high spatial frequency.
What is needed, therefore, is a diffraction grating structure configured for modulating a low spatial frequency light into a high spatial frequency light and a method for manufacturing the same.